1. Field of the Invention
The present invention relates to control of a DC/DC converter for increasing or decreasing a direct current voltage.
2. Description of the Related Art
A DC/DC converter is conventionally used to obtain, from a direct current power source, a direct current voltage which differs from the output voltage of the power source. For example, in hybrid vehicles and electric vehicles, while a high voltage is desired for efficient high-load drive of a motor, it is preferable that the voltage of a battery which serves as the power source be as low as possible. For this reason, a system has been proposed for boosting a battery voltage by means of a DC/DC converter for use as a power source for a motor. Further, DC/DC converters are widely employed in many other cases in which two or more direct current power sources are required. An example DC/DC converter control system is described in Japanese Patent Laid-Open Publication No. 2004-120844. A system according to this publication performs control without using a current sensor.
In this type of system, feedback control is performed with respect to a duty ratio concerning a pair of switches for connecting a terminal of a reactor alternately to the power source and ground. More specifically, the output voltage is measured, and the duty ratio is controlled (by PI control, for example) in accordance with a difference between the measured output voltage and a target voltage, thereby achieving the feedback control.
In typical cases, the output voltage can be controlled to the target value by such a feedback control. However, when the target value is varied or when the state of load changes greatly, a more precise control is necessary.